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mm: clarify __add_to_swap_cache locking 

__add_to_swap_cache unconditionally sets the page locked, which can be a bit
alarming to the unsuspecting reader: in the code paths where the page is
visible to other CPUs, the page should be (and is) already locked.

Instead, just add a check to ensure the page is locked here, and teach the one
path relying on the old behaviour to call SetPageLocked itself.

[hugh@veritas.com: locking fix]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin 2007-10-16 01:24:42 -07:00 committed by Linus Torvalds
parent 45726cb43d
commit b55ed81623
1 changed files with 4 additions and 1 deletions
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5
mm/swap_state.c
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@ -74,6 +74,7 @@ static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
{
int error;
BUG_ON(!PageLocked(page));
BUG_ON(PageSwapCache(page));
BUG_ON(PagePrivate(page));
error = radix_tree_preload(gfp_mask);
@ -83,7 +84,6 @@ static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
entry.val, page);
if (!error) {
page_cache_get(page);
SetPageLocked(page);
SetPageSwapCache(page);
set_page_private(page, entry.val);
total_swapcache_pages++;
@ -99,15 +99,18 @@ static int add_to_swap_cache(struct page *page, swp_entry_t entry)
{
int error;
BUG_ON(PageLocked(page));
if (!swap_duplicate(entry)) {
INC_CACHE_INFO(noent_race);
return -ENOENT;
}
SetPageLocked(page);
error = __add_to_swap_cache(page, entry, GFP_KERNEL);
/*
* Anon pages are already on the LRU, we don't run lru_cache_add here.
*/
if (error) {
ClearPageLocked(page);
swap_free(entry);
if (error == -EEXIST)
INC_CACHE_INFO(exist_race);